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TPS563211: power circuit generate audible sound only when placed on surface at specific angle

Ning LU
Prodigy 70 points
Part Number: TPS563211
Other Parts Discussed in Thread: TPS65235, TPS65235-1

Hi,

I use TPS563211 to convert input 5~10V to 3.3V, exact the same circuit as reference design in datasheet. 

The circuit works but, when the board is laid on top of a flat surface, like a table, it will generate audible sound, and it looks come out from the inductor. However, when the board is like handheld or mounted on a rack, no sound can be heard. 

What could be the possible reason?

Thank you.

/Roland

  • 0
    TI__Expert 8100 points

    Hi Ning,

    Could you please help to share your layout and waveforms of Vin+Vout+SW+IL?

    Could you please help to share loading condition of TPS563211?

    BRs

    Zixu

  • 0 in reply to Zixu Wang
    Prodigy 70 points

    Thanks for the quick response.

    Please check the layout screen shot as following,

    The load current when doing the test is very small, under 100mA.

    I have not tested the waveform yet. I will do it later then upload.

    /Roland

  • 0 in reply to Ning LU
    TI__Genius 13451 points

    Hi Roland!
    It is possible that there are some low-frequency electrical signal which is lower than 20KHz. That is the reason why we need some waveform to confirm this. 

    SHUAI

  • 0 in reply to Shuai Fan
    Prodigy 70 points

    The waveform as below screenshot, very similar when open circuit or small load current less than 100mA.

    Also the schematic so you can double check,

    The interesting point is, there is audible sound only when I lay this board on flat surface. When I hold it or mount it in vertical position no sound can be heard.

    /Roland

  • 0 in reply to Ning LU
    TI__Expert 8100 points

    Hi Roland,

    I will analyze it and give you reply next week!

    BRs

    Zixu

  • 0 in reply to Ning LU
    TI__Expert 8100 points

    Hi Roland,

    From your shown waveform of Vout ripple, fsw is about 666Hz for such operation, which enters the range of audible noise of human beings.

    Such audible signal could cause vibration in inductor and output MLCC, which could cause audible noise. Principle could be referred to following AN:

    Introduction to Anti-Audible Noise Function in TPS65235-1

    If you have board in flat surface, audible signal could cause stress in board and it could not be transferred outside the board, which causes vibration in inductor or Cout. But if the board is mounted or handheld, board has solid interface to transfer stress outside of the board, which will not cause vibration in inductor or Cout.

    BRs

    Zixu

  • 0 in reply to Zixu Wang
    Prodigy 70 points

    Zixu,

    thank you for the explanation and the reference link.

    Can I ask how you derived the 665Hz from the waveform? 

    And, the reference link takes TPS65235 as an example, showing that BOOST cap is the root cause. Is it the same reason in this case? 

    /Roland

  • 0 in reply to Ning LU
    TI__Expert 8100 points

    Hi Roland,

    Sorry for mis-calculation, fsw is about 250Hz. Since it is AC couple in oscilloscope, supposing your measure output voltage ripple. One big div for 2.5ms from your figure, which means 0.5ms for small div.

    For one cycle of Vout ripple, it has 1 big div + 3 small div, which is about 4ms for period and 250Hz fsw. Such fsw has already entered audible range of humans.

    For your second question: Yes, it is the same reason with this case.

    BRs

    Zixu

  • 0 in reply to Zixu Wang
    Prodigy 70 points

    Zixu,

    thank you for detailed answer.

    However, The solution in TPS65235 AN is a different IC TPS65235-1, which canceled internal OVP comparator so the ripple frequency changed. How can I apply the fix in my case?

    /Roland

  • 0 in reply to Ning LU
    TI__Expert 8100 points

    Hi Ning,

    FCCM operation could be used to eliminate audible noise. In FCCM operation, 563211 always works with 600kHz fsw no matter what loading applied.

    Please refer to following table in ds for reference.

    BRs

    Zixu